apt-get update GPG error: Internal error: Good signature, but could not determine key fingerprint?!

[iain@thargoid.co.uk]

Hello all

  I am seeing a rather strange error. I have a wheezy VM which I am 
trying to update, but I get the above error on the main source and also 
on security source:

W: GPG error: http://security.debian.org wheezy/updates Release: 
Internal error: Good signature, but could not determine key 
fingerprint?!
W: GPG error: http://mirror.ox.ac.uk wheezy Release: Internal error: 
Good signature, but could not determine key fingerprint?!

Attempting to re-install gnupg and also debian-archive-keyring make no 
difference. Trying a new mirror also makes no difference. Same error.

Anyone seen this before, or perhaps knows more about GPG than me to help 
me in the right direction?

Other VM's update no questions asked

Cheers

Iain